A lithographic apparatus is a machine that applies a desired pattern onto a substrate, usually onto a target portion of the substrate. A lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs). In that instance, a patterning device, which is alternatively referred to as a mask or a reticle, may be used to generate a circuit pattern to be formed on an individual layer of the IC. This pattern can be transferred onto a target portion (e.g. comprising part of, one, or several dies) on a substrate (e.g. a silicon wafer). Transfer of the pattern is typically via imaging onto a layer of radiation-sensitive material (resist) provided on the substrate. In general, a single substrate will contain a network of adjacent target portions that are successively patterned. Known lithographic apparatus include so-called steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion at one time, and so-called scanners, in which each target portion is irradiated by scanning the pattern through a radiation beam in a given direction (the “scanning”-direction) while synchronously scanning the substrate parallel or anti-parallel to this direction. It is also possible to transfer the pattern from the patterning device to the substrate by imprinting the pattern onto the substrate.
In addition to EUV radiation, radiation sources used in EUV lithography generate contaminant material that is harmful for the optics and the working environment wherein the lithographic process is carried out. Such is especially the case for EUV sources operating via a laser induced plasma. Hence, in EUV lithography, a desire exists to limit the contamination of the optical system that is arranged to condition the beams of radiation coming from an EUV source. Furthermore, it can be desirable to provide spectral filtering to the radiation coming from the EUV source since in addition radiation may be produced which is preferably kept out of the optical path downstream of the radiation source, especially the illumination system and projection system which are used for conditioning an EUV radiation beam and projecting said beam onto a substrate, respectively. To spectrally filter an EUV radiation beam a variety of materials are known which can provide such filter function, however, due to the debris traveling from the EUV source, the positioning of such materials in the optical path can be problematic.